Reference to Co-pending Application
Reference is hereby made to a co-pending patent application assigned to the same assignee as the present application entitled: "Diffusion Tip for Optical Fibers," filed on Nov. 1, 1990 under Ser. No. 07/608,006.
1. Field of the Invention
This invention relates to an apparatus for delivering light to and from a target situated along the wall of a tortuous tube. More particularly, the invention relates to an improved catheter for delivering light for photodynamic therapy of atherosclerosis or for receiving an optical signal from the wall of a blood vessel which may be comprised of healthy tissue, atherosclerotic plaques, thrombus, calcium or any combination thereof.
2. Prior Art
Approximately four million people in the United States suffer from arteriosclerotic coronary artery disease. Many of these people are likely to suffer or die from myocardial infarction, commonly known as heart attack. Heart disease is, in fact, the leading cause of death in the United States. Thrombosis in the coronary artery beyond the arteriosclerotic constriction is the usual cause of heart attacks. A procedure which can open arteriosclerotic constrictions thereby permitting the normal flow of blood to the heart may reduce the many deaths and disabilities caused by heart disease.
Constrictions in the coronary artery are caused by a buildup of plaque. Plaque can occur in many forms, from a thick viscous consistency (similar to toothpaste) to a rock-hard consistency depending on the proportion of components which may include calcium, fibrous tissue, fatty deposits, organized clots and thrombus.
These deposits accumulate at one location and drastically narrow the bore of the artery thus restricting and even totally blocking the flow of blood. The site of accumulated deposits that constitute a blood vessel is referred to as stenosis while a total blockage is referred to as occlusion. Various techniques such as arterial bypass surgery, endarterectomy, balloon angioplasty and drilling procedures have been employed for removing deposits of plaque. If the plaque is of recent origin and is reasonably elastic, a balloon catheter may be used to clear the artery.
Percutaneous Transluminal Coronary Angioplasty (PTCA), described in U.S. Pat. No. 4,195,637 to Gruntzig et al issued Apr. 1, 1980 has been utilized for a number of years to treat coronary arteries narrowed by plaque deposits. A catheter having inflatable balloon secured to its distal end is advanced through an artery to a narrowed region. The balloon is then inflated with a fluid from an external source, causing the narrowed region of the artery to be expanded. The balloon is then deflated and withdrawn. A serious problem associated with balloon angioplasty has been the occurrence in up to 30% of the cases of so-called restenosis, either immediately after the procedure or within about six months. Another problem associated with PTCA is abrupt closure. This results from flaps or segments of healthy and plaque-ridden vessel wall which are formed during balloon angioplasty by the balloon catheter advancing sub-intimally and which can block the artery. Such blockage of the artery requires emergency surgery and can often result in death. Furthermore, a surgical team is required to stand by during the balloon angioplasty procedure.
To overcome the problem of abrupt closure, the flaps or segments of detached intima which are formed during the balloon angioplasty and which block the artery can be fused by heating either the wall of a special balloon in a procedure called laser balloon angioplasty (LBA) sufficiently to cause fusion of the tissue or by the passage of a hot laser tip through the expanded vessel to cause fusion.
Other techniques involving the application of heat in a coronary artery include the "hot tip" described in U.S. Pat. No. 4,646,737 issued Mar. 3, 1987 to Hussein et al and U.S. Pat. No. 4, 662,368 issued May 5, 1987 to Hussein et al wherein a thermally conductive tip located at the end of a catheter is heated by laser radiation and conducts heat to the surrounding region as it is pushed through a narrowed artery. The hot tip reaches temperatures on the order of several hundred degrees Celsius in order to produce the necessary conductive heating as it is pushed through the artery. The hot tip is unable to expand the artery beyond the conductive tip diameter, which must be limited by the introduction site lumen and by the caliber of the artery being treated. Moreover, most total stenoses or occlusions and totally calcified blockages cannot be treated by balloon angioplasty. Even a "hot tip" catheter cannot open up a totally calcified blockage.
Prior art techniques have been disclosed for directing laser radiation outwardly from the tip of an optical fiber to vaporize plaque. An optical fiber surrounded with a scattering medium for producing a cylindrical pattern of light at the tip of an optical fiber is disclosed in U.S. Pat. No. 4,660,925 issued Apr. 28, 1987 to McCaughan, Jr. and in copending U.S. patent application Ser. No. 07/608,006. None of the prior art techniques taken alone provide the combination of small diameter, flexibility, power handling capability and compatibility with a guide wire necessary for the permanent removal of plaque from a blood vessel.
Spears, in U.S. Pat. No. 4,773,899 issued Sep. 27, 1988, incorporated herein by reference, teaches the administration of a hematoporphyrin, preferably by intravenous injection to an atherosclerotic patient to be treated. The hematoporphyrin when administered intravenously, is selectively absorbed into the atheromatous plaque, with little or no absorption into healthy areas of the arterial wall. Upon illumination of the atheromatous plaque containing the exogenous chromophore, the hematoporphyrin is activated. The activated hematoporphyrin facilitates the destruction and sloughing off of the host atheromatous plaque tissue.
Illumination of the plaque has been achieved by different techniques. With one technique, the method for which the present invention is particularly well suited, the patient is catheterized with a light-emitting catheter inserted into the diseased vessel so that the light-emitting portion of the catheter is adjacent to the atheromatous plaque. Alternatively, a form of liquid light such as firefly luciferin-luciferase is injected into the vasculature such that the liquid light, which mixes freely with blood or blood replacement, perfuses the diseased artery.
Spears, in U.S. Pat. No. 4,512,762, teaches the use of a special light-emitting balloon catheter for photoatherolytic therapy (PAT). The balloon catheter includes (a) an inflatable balloon secured to one end of the catheter tube for inflation with a gas or liquid from a remote source, and (b) at least one optical fiber which extends through the catheter lumen for transmission of light from an external light source to the interior of the balloon, and (c) a light-scattering device within the balloon in the form of a hollow, liquid-filled tube. The liquid filling the tube is selected for optimal transmission of light and maximum light scattering.
Use of Spears balloon catheter provides for a more or less transparent optical path between the diffuser and the plaque by displacement of the blood (which is opaque to light at short visible wavelengths) between the external balloon surface and the arteriosclerotic plaque by inflation of the balloon. In operation, Spears' catheter stems the flow of blood along a vessel and requires intermittent and cyclical illumination-inflation/deflation of the balloon so as to minimize interruption of blood flow to the vital organs and to avoid potential problems due to heating of the balloon material and the blood of the patient undergoing treatment. In view of the growing use of PAT and the shortcoming of the prior art devices, it is desirable to provide a light delivery system which: (a) can be advanced over a guidewire; and (b) is sufficiently supple to be able to follow a tortuous path; (c) does not require inflation of a balloon to interrupt blood flow during illumination; and (d) can receive light emitted by a target tissue for fluorescence detection.